The 1000 Chinese lumens torches with handlebar mounts seem to be getting popular round here. £20 or so, with two 3.7v li-ion cells & a charger. Heavier on the bars, of course.
The Magicshine clones should work perfectly well with a 6 volt battery (e.g. a standard Nimh pack, of which I have a few old but still sound ones), BTW. Real Magicshine lights do. A little dimmer than at 7.4V, & it confuses the battery low indicator, but the light is happy to go on shining. The light head has a much lower voltage cut-off than the Li-ion battery, & the battery low indicator shows what it thinks the state of a Li-ion battery is, from the voltage.